Add the vanilla, then add half of the flour. Mix until combined, then add the rest of the flour and mix until you have a smooth cake batter. Divide the batter equally between 6 medium-sized bowls ...
Beat until smooth and thick. Spoon the cake batter into the prepared tin. Top with the rhubarb, pressing it down gently. Sprinkle with the reserved 3 tablespoons of sugar. Bake for 1 hour 15 ...